The instant invention relates to a process for piecing to an open-end friction spinning device in which a yarn is back-fed into the nip, is connected therein with fibers and is then again drawn off continuously from said nip. The invention also relates to a device to carry out such process.
When a yarn breaks, or following a stoppage of the spinning process due to other causes, the feeding device is immediately stopped in order to prevent unnecessary fiber feeding which would clog and damage the spinning device. However, the opening roll continues to run as a rule, since stopping it separately for each spinning station would not only require a great technical effort, but starting and slowing down would take up a considerable amount of time. As a consequence, the fiber tuft which extends from the stopped feeding device into the range of the opening roll would be completely removed.
Based on the recognized fact that each stoppage of the feeding device causes a certain amount of damage of the fiber tuft, depending on the duration of the stoppage, proposals have been made in the past to divert the stream of fibers on its way to the fiber collecting surface and to guide it past the fiber collecting surface into a suction device. For this purpose, suction openings (see British patent publication 1,170,869 corresponding with U.S. Pat. No. 3,521,440) or compressed air openings (see German patent publication 3,104,444 corresponding with U.S. Pat. No. 4,384,451) have been provided in the feeding channel. Although undamaged fibers are fed precisely at the desired moment to the fiber collecting surface thanks to the uninterrupted fiber feeding and opening process, such openings within the highly sensitive fiber conveying path between the opening roll and the fiber collecting surface interfere with the spinning process. None of these proposals were therefore of practical significance.
It is the object of the instant invention to create a process and a device for piecing to an open-end friction spinning device which makes it possible to carry out faultless and secure piecing without affecting the subsequent spinning process.
This objective is achieved according to the invention in that the fibers are fed continuously to the nip but are then first taken out of the nip, in that the friction spinning elements are driven in spinning direction and in that the removal of the fibers is ended, in that the yarn end is back-fed to the forming accumulation of fibers and in that the yarn is drawn off from the nip while the fibers fed to said nip are continuously incorporated into the yarn. The removal of the fibers from the nip causes first of all those fibers which had been damaged through stoppage of the feeding device while the opening roll continues to run to be removed. Then, when the removal of the fibers from the nip during continuous feeding of fibers into the nip is ended, the undamaged fibers are deposited on the friction spinning elements and constitute a fiber accumulation there which is incorporated into the yarn end after said yarn end is back-fed, thus producing a piecing joint of great strength.
According to a preferred process, the fibers are brought through the nip onto the side of the friction spinning elements away from the nip, and are removed from there. In this way it is not necessary, for their removal, to greatly change the path of the fibers coming out of the fiber feeding channel. To remove the fibers it is advantageous if the spinning element normally rotating out of the nip is reversed in its rotation and is then again returned to its normal direction of rotation so that it again rotates out of the nip in order to terminate the removal of the fibers from the nip. Removal of the fibers if preferably effected by pneumatic, not by mechanical means.
Instead of going through the nip, the fibers can also be sucked away at a parallel to the nip, with a suction nozzle being used on the side of the friction spinning elements opposite to the draw-off side. The aspiration of the fibers from the nip is preferably ended by simply switching off the negative pressure prevailing outside the friction spinning elements.
For the removal of the fibers the two friction spinning elements are preferably spread apart in a radial direction, so that the fibers are removed in the simplest manner through the nip. In this case it is best if the two friction spinning elements are cleaned by being spread apart and by switching off the suction airstream from the friction spinning element which is subjected to suction, with the negative air pressure being again applied to the friction spinning element capable of being subjected to suction only when the two friction spinning elements have been returned into operating position.
In the sense of the instant invention, the "operating position" is understood to mean a position of the friction spinning elements which makes it possible to collect fibers in the nip formed by such elements and to incorporated them into a yarn end. For example, the friction spinning elements can in this case be so close to each other that the accumulation of fibers takes place in the nip on the fiber feeding side; depending upon the configuration of the open-end friction spinning device, it is however also possible to set the operating position so that the fibers are fed into a first nip on one side of the plane defined by the axles of the two friction spinning elements and are incorporated into the end of a yarn in a second nip which is constituted by the friction spinning elements on the other side of that plane.
To be able to control the stream of fibers to be spun into the yarn end, removal of the fibers is preferably not terminated suddenly, but instead gradually.
Since the back-feeding of the yarn into a readiness position for piecing, at least in its last phase, is normally carried out or assisted pneumatically, there is a danger, while fiber feeding is switched on, for the fibers to be sucked towards the yarn end and to attach themselves to it. When this occurs, no well-defined yarn end is available at the moment of piecing. To avoid this, a further variation of the process according to the instant invention provides for the yarn to be first brought into a readiness position outside the nip for piecing. This ensures that the fibers are brought into contact with the back-fed yarn end only at the desired moment, during the piecing process. Preferably, back-feeding of the yarn is controlled in such a manner that the yarn end is laid on the forming accumulation of fibers. In principle the friction spinning elements do not yet have to be driven in spinning direction before the introduction of the yarn into the nip, but it has been proven best if they are driven in spinning direction at the latest when the removal of the fibers from the nip is ended.
To carry out the process, the invention provides for a controllable air suction nozzle directed against the nip to be attributed to the fiber feeding channel. The air suction nozzle assigned to the fiber feeding channel has the role of sucking away the fibers from the nip for as long as said fibers are not yet to remain in the nip for incorporation into a yarn end.
According to a simple embodiment of the object of the invention the suction air nozzle can be located at the rear (with respect to the direction of yarn draw-off) of the friction spinning elements.
Preferably the suction air nozzle is arranged at that side of the friction spinning elements which is opposite the fiber feeding channel.
In this way the fibers to be removed need not be diverted on their way into the suction air nozzle.
In order to avoid an additional source of negative pressure for this suction air nozzle, the possibility should preferably be provided to switch the negative pressure from the suction air nozzle to the friction spinning element capable of being subjected to suction and back again. If a piecing device capable of travelling alongside a plurality of open-end friction spinning devices is provided, it is preferable if the negative pressure in the suction air nozzle and in the friction spinning element capable of being subjected to suction can be controlled from such travelling piecing device.
To be able to control the required flow of fibers required for piecing, a further preferred variation of the invention provides for the possibility of gradually adjusting the negative pressure taking effect in the suction air nozzle.
To remove the fibers from the nip, the friction spinning element rotating out of the nip can be provided with a controllable reversing clutch. The reversing clutch can be used to drive the friction spinning element rotating out of the nip during the spinning process temporarily in the direction of the nip, as is the case for the other friction spinning element. In this way, the fibers fed to the nip are fed through between the friction spinning elements, to be removed pneumatically or by means of a conveyor belt on the other side.
Alternately or in addition, the two friction spinning elements can also be designed so that they can be moved radially in relation to each other for the removal of the fibers.
To define different reproducible spinning positions for the open-end friction spinning device in a simple manner, the operating position of the two friction spinning elements can be set by means of a stop in another embodiment of the object of the invention.
To provide in a simple manner synchronization between the discontinuance of negative pressure in the suction air nozzle which removes the fibers and application of same to the friction spinning element or elements, an advantageous embodiment of the device according this invention provides that the negative pressure can be switched from the suction air nozzle to the friction spinning element capable of being subjected to suction and vice versa.
To prevent extraneous air from entering the housing in which the friction spinning elements are located, the method of bearing the movably supported friction spinning element is preferably constituted by a housing part which is supported on bearings and can be moved in relation to a housing part bearing the fixedly supported friction spinning element.
Since the position of the friction spinning elements determines whether the fibers are sucked away or are deposited in the nip on the friction spinning elements, the negative pressure in the suction air nozzle and in the friction spinning element capable of being subjected to the suction is preferably controllable in function of the position of the friction spinning elements.
The yarn end should not reach the nip for as long as the fibers are sucked out of said nip so that no fibers can attach themselves to the yarn end, as this would result in an undefined yarn end. For this reason, the yarn end is not fed directly to the nip but is fed by means of the friction spinning element rotating into the nip. For this purpose the invention provides for the housing to be provided with a yarn insertion slit facing the circumferential surface of the friction spinning element rotating into the nip. For this it is preferable for the friction spinning element turning into the nip to be fixedly supported, while the friction spinning element rotating out of the nip is movably supported in relation to the other friction spinning element. In this way the yarn can be deposited on the rotating friction spinning element even before the two friction spinning elements have again come into contact with each other.
The process and the device according to the invention makes it possible in a simple and secure manner for undamaged fibers to reach the nip of the open-end spinning device without any intervention in the fiber conveying path between delivery device and open-end friction spinning element being necessary. Thanks to the possibility of using undamaged fibers in the piecing process, a smaller amount of fiber suffices to achieve a given strength of the piecing joint than if damaged fibers must be used in said piecing joint. An unobtrusive piecing joint is the result. Since no interventions of any kind are required in the fiber conveying path, the quality of the yarn produced also remains unaffected, so that the piecing joint as well as the yarn produced following it have a good aspect and possess great strength.